In certain applications, it is often necessary to apply an accurate amount of an adhesive to bond a part to a workpiece. Many adhesive containers are designed so that a relatively accurate amount of adhesive can be dispensed from the container under manual squeeze pressure. A variety of dispensing apparatuses such as pumps and guns, which are designed to easily and accurately dispense a measured amount of adhesive.
In certain situations, due to the nature of the adhesive employed, it is necessary to design the dispensing mechanism to assure that the components of the mechanism do not come in contact with the adhesive itself. Depending upon the adhesive, such contact may either adversely effect the adhesive, adversely effect the components of the dispensing apparatus, or both. Such a situation is particularly evident with the use of cyanoacrylate (“CA”) adhesives.
In such situations, it has been common to use a peristaltic pump to dispense the adhesive from a container. A peristaltic pump is a positive displacement pump used to dispense fluid from a container through a flexible tube. Peristaltic pumps are typically used to pump various fluids, such a clean or sterile fluid, where there is a desire for the pump not to contaminate the fluid, or to pump aggressive fluids, such as adhesives so that the fluid cannot contaminate the pump. However, as the peristaltic pump operates under closed conditions, the container for the fluid must be a collapsible container so that as the fluid is pumped from the container the container will collapse around the remaining contents thereof.
In situations where fluid is provided in a rigid non-collapsible container, the use of a peristaltic pump becomes difficult inasmuch as air cannot enter the rigid container to replace the volume of fluid dispensed. Venting the rigid container directly to atmosphere is not a viable option where the fluid is an adhesive such as a CA adhesive which cures in the presence of air. This has resulted in the inability to dispense such adhesives from a sealed rigid container using a peristaltic pump.